Studies of the biology of the immune response of newborns to ingested antigens showed that anti-milk protein (BSA) immune responses in young rabbits (kits) were depressed if the mother had previously ingested BSA (po immunized). This immune regulation was antigen specific and did not occur if the dam was parenterally immunized. The presence of antibody in milk or of detectable antigen or antibody in the serum of the dam or kit did not correlate with the observed regulation of the immune responses. Kits will be cross suckled between po immunized and unimmunized dams to determine whether this regulation is transmitted in utero or in milk. Isolation and characterization of a soluble factor by immunochemical methods or of a cell by density gradient, adherence and similar fractionation techniques will be attempted. Wider applicability of such regulation will be examined by feeding rabbits diphtheria toxoid or respiratory syncytial virus and evaluating the immune respones of these kits to these two antigens. If this regulatory factor is transmitted in milk, it has important implications for the value of breast feeding. Identification of this factor in humans and its correlation with milk and soy protein intolerance (a form of food allergy) in infants will test the hypothesis that this common syndrome may be linked to immune regulation. Such regulation may be essential to the balance of newborn responses and its' absence could result in undue susceptibility to infection or mucosal damage induced by immune complexes. Further experiments to understand the maternal regulation and to enhance the immune response to ingested diphtheria toxoid include varying dosage and time of ingestion and oral administration of adjuvants (M.D.P.). This information should facilitate the development of an oral vaccine. Long-term goals include a better understanding of immune regulation and response in newborns, identification of deviations from the normal which may be associated with disease, and development of a widely applicable method for the immunization of newborns against bacterial toxins and cells. In countries with limited medical personnel, such a vaccine would be especially needed.